1. Field of the Invention
The present invention relates to a flap support mechanism for attachment of a flap to a helicopter rotor blade and to a flap-equipped rotor blade provided with the same.
2. Description of the Related Art
Rotation of a helicopter rotor blade causes action of centrifugal force proportional to a distance from the rotor center and to the square of a rotational velocity of the rotor. The centrifugal force at the tip of the blade can reach approximately 800 G to 1,000 G. When the rotor blade is provided with a flap, centrifugal force dependent on the mass thereof will act on the center of mass of the flap. It is therefore demanded of a flap hinge mechanism to ensure an angular displacement motion of the flap despite the large centrifugal force and the centrifugal moment corresponding to the distance from the hinge axis to the center of mass of the flap.
When a thrust bearing is used in the flap hinge mechanism, for example, so as to be able to withstand centrifugal force along the direction of the hinge axis, the large centrifugal force causes an increased frictional loss at the bearing and there is a dramatic reduction in flap output angle.
It is an object of the present invention to provide a flap support mechanism and a flap-equipped rotor blade that permits smooth flap motion in spite of a large centrifugal force.
The invention provides a flap support mechanism for angularly displaceable support of a flap attached to a helicopter rotor blade. The flap support mechanism comprises: a tension-torsion member disposed coaxial with an axis of angular displacement of a flap, wherein one end at a blade root side of the tension-torsion member is secured to the rotor blade, and the other end at a blade tip side thereof is secured to the flap.
In accordance with the invention, when centrifugal force acts on the flap during rotation of the rotor blade, a tension-torsion member coupling the rotor blade and the flap permits support of flap centrifugal force by means of tensile support of the tension-torsion member. Accordingly, the need for the flap hinge mechanism to employ a thrust bearing, for example, such as would be able to withstand centrifugal force can be eliminated, permitting elimination of frictional losses at the hinge. Moreover, because the tension-torsion member can also function as a torsion spring, disposing the tension-torsion member coaxial with the axis of angular displacement of the flap permits smooth angular displacement motion of the flap.
The tension-torsion member is sometimes called xe2x80x9ctension torsion straps,xe2x80x9d xe2x80x9ctorsion bars,xe2x80x9d and the like, and may be a rod-like, bar-like, fiber-like, wire-like, or laminate-like member formed of high-tensile-strength metal, fiber-reinforced plastic or the like. Because such a tension-torsion member produces almost no frictional loss, it is instrumental in improving flap drive system efficiency.
Furthermore, in the invention, it is preferable that the mechanism comprises a bearing possessing a rotational axis coaxial with an axis of angular displacement of the flap, for coupling the rotor blade and the flap.
In accordance with the invention, because centrifugal force is reduced and tensile supporting force of the tension-torsion member decreases when the rotor blade is stationary or is turning at low rotational velocity, provision of the bearing for coupling the rotor blade and the flap can prevent radial deviation from flap axis and sagging of the flap due to its own weight. Furthermore, because centrifugal force produced during rotation of the rotor blade is supported by the tension-torsion member, there is no increase in the axial (thrust) load on the bearing, permitting reductions in the size and weight of the bearing and elimination of nearly all of the frictional losses associated with the thrust bearing. Furthermore, in the invention, it is preferable that the tension-torsion member passes through a cavity formed at an interior of the flap and is secured to the flap at a location toward the blade tip.
In accordance with the invention, because torsional stroke increases with an increase of length of the tension-torsion member, a cavity is formed at the interior of the flap, and by arranging the tension-torsion member to pass through the cavity, it is possible to maximize the effective length of the tension-torsion member, permitting savings in space and reductions in size of the flap support mechanism.
Furthermore, the invention provides a flap support mechanism for angularly displaceable support of a flap attached to a helicopter rotor blade the flap support mechanism comprises first and second tension-torsion members being disposed coaxial with an axis of angular displacement of a flap, wherein one end at a blade root side of the first tension-torsion member is secured to the rotor blade, and the other end at a blade tip side thereof is secured to the flap, and one end at the blade root side of the second tension-torsion member is secured to the flap, and the other end at the blade tip side thereof is secured to a tension-applying mechanism.
In accordance with the invention, when centrifugal force acts on the flap during rotation of the rotor blade, the first tension-torsion member coupling the rotor blade and the flap permits support of flap centrifugal force by means of tensile support of the first tension-torsion member. Moreover, because the first tension-torsion member and the second tension-torsion member can also function as torsion springs, disposing the first and second tension-torsion members coaxial with the axis of angular displacement of the flap permits smooth angular displacement motion of the flap.
Furthermore, since the tension-applying mechanism is provided at the other end at the blade tip side of the second tension-torsion member, tensile forces of the first and second tension-torsion members can establish a stable flap axis of angular displacement. Accordingly, radial deviation from flap axis during operation of the flap is prevented.
The tension-torsion members are sometimes called xe2x80x9ctension torsion straps,xe2x80x9d xe2x80x9ctorsion bars,xe2x80x9d and the like, and may be rod-like, bar-like, fiber-like, wire-like, or laminate-like members formed of high-tensile-strength metal or fiber-reinforced plastic or the like. Because such a tension-torsion member produces almost no frictional loss, it is instrumental in improving flap drive system efficiency.
Furthermore, as the tension-applying mechanism may be employed a slide weight mechanism capable of movement in the blade spanwise direction, being the direction in which centrifugal force acts, or a preload mechanism whereby the tension-torsion member is previously loaded with tension at the time of installation of the tension-torsion member, or the like.
Furthermore, in the invention, it is preferable that the first tension-torsion member and the second tension-torsion member are mutually coupled.
In accordance with the invention, when the two ends of the flap are supported in tensile fashion by first and second tension-torsion members, mutual coupling of the first tension-torsion member to the second tension-torsion member can reduce tensile stress inside the flap, since the tensile load of the first and second tension-torsion members can no longer act directly on the flap.
Furthermore, in the invention, it is preferable that the mechanism comprises a stabilizer bearing for preventing radial deviation of the first tension-torsion member and second tension-torsion member.
In accordance with the invention, because centrifugal force is reduced and the tensile supporting force of a tension-torsion member decreases when the rotor blade is stationary or is turning at low rotational velocity, provision of the stabilizer bearing for preventing radial deviation of the first tension-torsion member and second tension-torsion member can prevent of radial deviation of flap axis and sagging of the flap due to its own weight. Furthermore, because centrifugal force produced during rotation of the rotor blade is supported by the tension-torsion members, there is no increase in the axial (thrust) load on the bearing, permitting reductions in the size and weight of the bearing.
Furthermore, in the invention, it is preferable that the mechanism comprises a tuning weight provided at the leading edge of the flap, for aligning a center of mass of the flap with the axis of angular displacement of the flap.
In accordance with the invention, the tuning weight is provided at the leading edge of the flap to align the center of mass of the flap with the axis of angular displacement of the flap. As a result, the moment about the flap axis of angular displacement arising due to inertial forces corresponding to the distance between the center of mass and the flap axis of angular displacement can be cancelled. Accordingly, the load on the flap drive system is reduced. In addition, application of the invention permits prevention of flap flutter.
Furthermore, the invention provides a flap-equipped rotor blade comprising the flap support mechanism as described above.
In accordance with the invention, a rotor blade capable of smooth flap motion in spite of large centrifugal force can be obtained because flap centrifugal force can be supported by means of tensile support of a tension-torsion member.